1. Field of the Invention
The present invention relates to an electroactive polymer actuator, which is preferably used for devices such as small-sized diaphragm pumps, and a diaphragm pump using the actuator.
2. Disclosure of the Prior Art
In the past, for devices such as small-sized diaphragm pumps, it has been proposed to use a laminate composed of a sheet of an electroactive polymer material such as silicon rubber and an acrylic material, and a pair of electrode layers formed on both surfaces of the sheet. When a voltage is applied between the electrode layers, a deformation of the laminate happens such that a dimension in the thickness (vertical) direction of the laminate decreases, and the dimension in the horizontal direction of the laminate increases. This phenomenon is known as electroactive effect.
For example, Japanese Patent Early Publication [kokai] No. 2001-263486 discloses a diaphragm pump using the electroactive effect. That is, as shown in FIG. 11, this diaphragm pump comprises a casing 1P having a concave 7P for providing a pump chamber in its top surface and intake and exhaust passages (2P, 3P), and a diaphragm 10P for covering this concave. The diaphragm 10P is of a laminate structure, which is formed with a thin-sheet member 12P of an electroactive polymer material, and a pair of electrode layers 11P formed on both surfaces of the thin-sheet member by a physical vapor deposition such as sputtering.
When a voltage is applied between the electrode layers 11P, a dimension in the thickness direction of the diaphragm 10P decreases and the dimension in the horizontal direction thereof increases. This brings a volume change of the pump chamber that is a space surrounded by the concave 7P and the diaphragm 10P. On the other hand, when the applied voltage is removed, the diaphragm 10P recovers its original shape. Therefore, according to this volume change of the pump chamber, it is possible to suck a fluid such as air into the pump chamber through the intake passage 2P, and then exhaust the air in the pump chamber the exhaust passage 3P. By applying a RF voltage having a required frequency between the electrode layers 11P, this pumping operation can be repeated.
However, in the case of using this laminate 10P as the diaphragm, it is difficult to control the deformation of the diaphragm during the pumping operation. Therefore, it still has plenty of room for improvement from the viewpoint of providing a stable and reliable pumping operation. In addition, since the diaphragm is formed by the laminate 10P including the single thin-sheet member 12P of the electroactive polymer material, there are problems that a deformation force of the diaphragm is relatively small, and a deformation speed thereof is relatively slow. These may lead to reductions in exhaust amount and response speed of the diaphragm pump. Thus, it is said that these problems are causes of preventing the actual use of the devices such as the small-sized diaphragm pump using the electroactive effect.